PUERTO MONTT, Chile (Reuters) - A towering plume of ash
from an erupting volcano in Chile's remote Patagonia could
collapse back down to devastate the surrounding area, a leading
expert warned on Friday.

Luis Lara, a geologist and volcano expert with the
government's geology and mining agency Sernageomin, says his
models show the vast column of ash, which has soared 7.5 miles

into the air, at a critical stage.

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A sudden collapse would shroud vast areas with hot gas, ash
and molten rock, killing anything in its way.

Authorities have evacuated thousands of people from the
immediate vicinity of Chaiten volcano, 760 miles south of the
capital Santiago, and are forcibly removing people within a 30
mile radius.

Chaiten began erupting eight days ago for the first time in
thousands of years.

"We are at a critical point of this phase given the
characteristics (of the eruption) have remained the same for
several days," Lara said.

"The volcano is now at its limit and one possibility is
that the column could collapse quickly, generating flows of
pyroclastic material down its ravines," he added. "But there
are also other scenarios, such as the energy of the eruption
being released more gradually."

In a worst case scenario, the flows of ash and fiery
material could reach the fjord Chaiten sits on, sending a
series of small waves fanning out toward settlements up to 125
miles away across the water.

Lara says the volcano could rumble on for years. He
suggested the town of Chaiten, 6 miles from the volcano and now
deserted, should be moved.

"In an ideal world, I would move the town somewhere else
more protected," Lara said. He would not risk living there.

The cloud has also caked towns on the Argentine side of the
border with ash. Satellite images show a white stripe smeared
across the continent.

However ash that had drifted as far as Buenos Aires
dissipated on Friday, and some airlines which canceled flights
overnight resumed service.

Chile is home to 2,000 volcanoes, 500 of which experts say
are potentially active. Around 60 have erupted over the past
450 years.